首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 0 毫秒
1.
小富勒烯研究进展   总被引:3,自引:1,他引:3  
对近年来C20,C24,C28,C32,C36,C40,C44和C50等小富勒烯及其内嵌、加成和取代衍生物的实验和理论研究进展进行了回顾,并对目前理论研究的热点C2n(n=26~29)进行了讨论.  相似文献   

2.
Four methanofullerene derivatives, with phosphonate or sulfone groups attached to a C(60) core through a Bingel procedure, were synthesized to probe their stability upon electrolytic reduction. Derivatives 1 and 2 are the most stable upon electroreduction and do not exhibit retro-cyclopropanation reactions until more than three electrons per C(60) derivative are transferred. The cyclopropane ring is then removed and C(60)(>CH(2))(n) (n=1-3) products result from reactions of the trianion of C(60) with the solvent, CH(2)Cl(2). The situation with diphosphonate 3 or phosphonatecarboxylate 4 is dramatically different. For 3, quantitative retro-cyclopropanation occurs when 2.8 e(-) per molecule are transferred. In the case of 4, when more than two electrons per molecule are transferred, there is evidence of the reversible formation of a very stable intermediate, which is oxidized at a potential 500 mV more positive than the first fullerene-based reduction of the parent compound. Electrolysis of a simple C(70)-Bingel monoadduct (5) also exhibits the formation of a similar intermediate. On the basis of cyclic voltammetry, ESR spectroscopy, and MALDI analysis of products, the intermediate observed during the electrolysis of compounds 4 and 5 is assigned to a dimeric structure.  相似文献   

3.
4.
    
Benzylpyridinium ions, generated via electrospray ionization of dilute solutions of their salts in acetonitrile/water, are probed by collisional activation in an ion-trap mass spectrometer. From the breakdown diagrams obtained, phenomenological appearance energies of the fragment ions are derived. Comparison of the appearance energies with calculated reaction endothermicities shows a reasonably good correlation for this particular class of compounds. In addition, the data indirectly indicate that at threshold the dissociation of almost all of the benzylpyridinium ions under study leads to the corresponding benzylium ions, rather than the tropylium isomers. Substituent effects on the fragmentation for a series of benzylpyridinium ions demonstrate that neither mass effects nor differences in density of states seriously affect the energetics derived from the ion-trap experiments.  相似文献   

5.
Four indole derivatives synthesized from 2-keto glycosides were analyzed by electrospray ionization tandem mass spectrometry (ESI-MSn) with low-energy collision-induced dissociation to establish a general structural elucidation of indole derivatives. Their fragmentation pathways are proposed on the basis of the MSn studies and deuterium-labeled experiments. Indole derivatives undergo complicated gas-phase rearrangements in addition to simple bond cleavages. A rearrangement, which involves a contraction of the six-membered ring, was observed and a mechanism was proposed. The observations may have some potential applications in the interpretation of the mass spectra of indole derivatives.  相似文献   

6.
7.
8.
    
The mass spectra of new substituted pyrrolidino[60]- and [70]fullerenes have been obtained using electrospray ionization conditions in the positive and negative mode of detection with two different mass spectrometers, a quadrupole ion trap and a Fourier transform ion cyclotron resonance. Radical anions M(●-) and deprotonated molecules [M-H](-) are formed under negative electrospray ionization mass spectrometry conditions, and the collision-induced dissociations of both ionic species have been studied. Either negative odd-electron ions or negative even-electron ions undergo a retro-cycloaddition process forming the corresponding fullerene product ions C(60)(●-) and C(70)(●-). The generation of fullerene radical anions from deprotonated molecules is a new exception of the \"even-electron rule.\" In contrast, the protonated molecules [M + H](+) obtained from the positive mode of detection do not undergo this cycloreversion reaction, and the MS(n) experiment reveals a variety of eliminations of neutral molecules involving different hydrogen shifts and multiple bond cleavages that lead eventually to substituted methanofullerene fragment ions. The observed fragmentations can be correlated with the electronic character of the substituents attached to the heterocyclic moiety. The results obtained from the thermal reactions of these compounds, carried out under different pH conditions, correlate well with those obtained in gas phase. The different behaviors between protonated and unprotonated molecules and ions can be explained assuming that the retro-cycloaddition reaction takes place only when the nitrogen atom of the pyrrolidine ring (the basic center of the molecule) is unprotonated both in gas and condensed phase. The protonation of the NH group inhibits the cycloreversion process, and therefore different fragmentations take place. The detailed mechanisms of the formation and evolution of the intermediate fragments are described.  相似文献   

9.
The mechanism of the Rh‐catalysed [2+2+2] cycloaddition reaction of diynes with monoynes has been examined using ESI‐MS and ESI‐CID‐MS analysis. The catalytic system used consisted of the combination of a cationic rhodium(I) complex with bisphosphine ligands, which generates highly active complexes that can be detected by ESI(+) experiments. ESI‐MS on‐line monitoring has allowed the detection for the first time of all of the intermediates in the catalytic cycle, supporting the mechanistic proposal based mainly on theoretical calculations. For all ESI‐MS experiments, the structural assignments of ions are supported by tandem mass spectrometry analyses. Computer model studies based on density functional theory (DFT) support the structural proposal made for the monoyne insertion intermediate. The collective studies provide new insight into the reactivity of cationic rhodacyclopentadienes, which should facilitate the design of related rhodium‐catalysed C? C couplings.  相似文献   

10.
《Analytical letters》2012,45(10):1972-1978
Abstract

Hexanitrohexaazaisowurzitane (CL‐20) is a newly developed propellant and has been examined using negative ion electrospray mass spectrometry. The primary ions observed included adduct ions (M+Cl) and (M+ONO2)?.  相似文献   

11.
通过直接进样方式,采用电喷雾电离质谱技术分析了8个合成的富勒烯-N-甲基吡咯烷衍生物,详细研究了其在电喷雾条件下的质谱行为。由结果可知,该类化合物在电喷雾电离过程中易得到电子而负离子化;当衍生物结构中有相对易质子化基团或有活泼氢时,则可获得质子化和去质子的正负离子谱图;衍生物在负离子模式下容易失去吡咯环产生富勒烯负离子,且在合适能量碰撞下易发生衍生化基团内部的逆环加成反应,通过失去1个中性小分子物质CH2‖N—CH3,产生新的一取代亚甲基富勒烯衍生物。基于电喷雾电离源技术联合离子阱分析器建立的质谱分析方法,不但能提供准确的分子量信息,还能通过获得高分辨同位素谱峰和丰富的二级碎片离子峰,进一步确认化合物的分子结构,是一种先进、快速的富勒烯吡咯烷衍生物定性分析方法。  相似文献   

12.
    
Electrospray ionization mass spectrometry/mass spectrometry in the positive ion mode was used to investigate the gas‐phase chemistry of multicharged ions from solutions of porphyrins with 1,3‐dimethylimidazolium‐2‐yl (DMIM) and 1‐methylimidazol‐2‐yl (MIm) meso‐substituents. The studied compounds include two free bases and 12 complexes with transition metals (Cu(II), Zn(II), Mn(III), and Fe(III)). The observed multicharged ions are either preformed or formed during the electrospraying process by reduction or protonation and comprise closed‐shell and hypervalent mono‐radical and bi‐radical ions. The observed extensive and abundant fragmentation of the DMIM and MIm meso‐substituents is a characteristic feature of these porphyrins. Fragments with the same mass values can be lost from the meso‐substituents either as charged or neutral species and from closed‐shell and hypervalent radical ions. Reduction processes are observed for both the free bases and the metallated DMIM porphyrins and occur predominantly by formation of hypervalent radicals that fragment, at low energy collisions, by loss of methyl radicals with formation of the corresponding MIm functionalities. These findings confirm that, when using electrospray ionization, reduction is an important characteristic of cationic meso‐substituted tetrapyrrolic macrocycles, always occurring when delocalization of the formed hypervalent radicals is possible. For the Fe(III) and Mn(III) complexes, reduction of the metal centers is also observed as the predominant fragmentation of the corresponding reduced ions through losses of charged fragments testifies. The fragmentation of the closed‐shell ions formed by protonation of the MIm porphyrins mirrors the fragmentation of the closed‐shell ions of their DMIM counterparts. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

13.
14.
    
According to the isolated pentagon rule (IPR), for stable fullerenes, the 12 pentagons should be isolated from one another by hexagons, otherwise the fused pentagons will result in an increase in the local steric strain of the fullerene cage. However, the successful isolation of more than 100 endohedral and exohedral fullerenes containing fused pentagons over the past 20 years has shown that strain release of fused pentagons in fullerene cages is feasible. Herein, we present a general overview on fused‐pentagon‐containing (i.e. non‐IPR) fullerenes through an exhaustive review of all the types of fused‐pentagon‐containing fullerenes reported to date. We clarify how the strain of fused pentagons can be released in different manners, and provide an in‐depth understanding of the role of fused pentagons in the stability, electronic properties, and chemical reactivity of fullerene cages.  相似文献   

15.
Abstract

Two new calixarene derivatives: 5,11,17,23-tetra-t-butyl-25,26,27,28-tetrakis-(piperidinocarbo-nylmethyoxy)calix[4]arene (L4) and 5,11,17,23,29,35,41,47-octa-t-butyl-49,50,51,52,53,54,55, 56-octa-(piperidinocarbonylmethoxy)calix[8]arene (L8), which show good binding abilities to metal ions, were synthesized by the reaction of the corresponding calixarene derivatives with piperidine. The ligand L4 is capable of separating a tight ion-pair formed by Pb2+ and the picrate anion in THF. The interactions of the new ligands (Ln n = 4, 8) with Na+, Pb2+ and Cd2+, in the presence or absence of picrate, were investigated by 1H NMR and electrospray mass spectrometry. It is found that L4 reacts with these metal ions to form a unique complex which can be described as [Mm+L4]m+ while L8 forms a variety of complexes depending on whether there are picrate anions in solution. [Mm+L8]m+ is formed in the absence of the picrate, and two complexes, [PbL8]·CH3CN·H2O and [PbNaL8]3+, are formed in the presence of the picrate. The higher conformational flexibility and larger macro-ring size of L8 account for the fact that it forms a variety of complexes as compared with L4.  相似文献   

16.
    
Porphyrin derivatives having a galactose or a bis(isopropylidene)galactose structural unit, linked by ester or ether bonds, were characterized by electrospray tandem mass spectrometry (ES-MS/MS). The electrospray mass spectra of these glycoporphyrins show the corresponding [M + H](+) ions. For the glycoporphyrins with pyridyl substituents and those having a tetrafluorophenyl spacer, the doubly charged ions [M + 2H](2+) were also observed in ES-MS with high relative abundance. The fragmentation of both [M + H](+) and [M + 2H](2+) ions exhibited common fragmentation pathways for porphyrins with the same sugar residue, independently of the porphyrin structural unit and type of linkage. ES-MS/MS of the [M + H](+) ions of the galactose-substituted porphyrins gave the fragment ions [M + H - C(2)H(4)O(2)](+), [M + H - C(3)H(6)O(3)](+), [M + H - C(4)H(8)O(4)](+) and [M + H - galactose residue](+). The fragmentation of the [M + 2H](2+) ions of the porphyrins with galactose shows the common doubly charged fragment ions [porphyrin + H](2+), [M + 2H - C(2)H(4)O(2)](2+), [M + 2H - C(4)H(8)O(4)](2+), [M + 2H - galactose residue](2+) and the singly charged fragment ions [M + H - C(3)H(6)O(3)](+) and [M + H - galactose residue](+). The fragmentation of the [M + H](+) ions of glycoporphyrins with a protected galactosyl residue leads mainly to the ions [M + H - CO(CH(3))(2)](+), [M + H - 2CO(CH(3))(2)](+), [M + H - 2CO(CH(3))(2) - CO](+), [M + H - C(10)H(16)O(4)](+) and [M + H - protected galactose](+). The doubly charged ions [M + 2H](2+) fragment to give the doubly charged ions [porphyrin + H](2+) and the singly charged ions [M + H - protected galactose residue](+) and [M + H - CO(CH(3))(2)](+). For the porphyrins where the sugar structural unit is linked by an ester bond, [M + 2H](2+), ES-MS/MS showed a major and typical fragmentation corresponding to combined loss of a sugar structural unit and further loss of water, leading to the ion [M + 2H - sugar residue - H(2)O](2+), independently of the structure of the sugar structural unit. These results show that ES-MS/MS can be a powerful tool for the characterization of the sugar structural unit of glycoporphyrins, without the need for chemical hydrolysis.  相似文献   

17.
18.
    
A novel mass spectrometric method is applied to rapid, accurate, quantitative analysis of chiral phenylglycine. Transition-metal-bound complex ions containing the chiral phenylglycine are generated by electrospray ionization mass spectrometry and subjected to collision-induced dissociation. The ratio of the two competitive dissociation rates is related to the enantiomeric composition of the mixture, allowing the determination of enantiomeric contamination in the intermediates.  相似文献   

19.
20.
The zinc complexes of diaryl bis(p-nitrophenyl)porphyrins and beta-(1,3-dinitroalkyl)tetraphenylporphyrins were studied by electrospray ionization (ESI) tandem mass spectrometry (MS/MS). All porphyrins showed the protonated molecule under ESI conditions. The protonated molecules were induced to fragment and the corresponding ESI tandem mass spectra were analysed. Porphyrins with two p-nitrophenyl groups showed, as expected, characteristic fragmentations including either loss of one nitro group, as the major fragment of the tandem mass spectra, and loss of both nitro groups. In contrast, MS/MS of the beta-(1,3-dinitroalkyl)porphyrins provided interesting and unexpected results such as the absence (or in insignificant abundance) of the ions formed by loss of one nitro group. However, these porphyrins show an abundant fragment due to combined loss of the two nitro groups. Also, the typical beta-cleavage of the alkyl chain is not observed per se, only when combined with loss of HNO2 or *NO2. Instead, alpha-cleavage, with loss of the beta-pyrrolic substituent, is the most favourable process.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号